Single-sideband FM is an advantageous transmission technique particularly for narrowband applications such as mobile telephony, telemetry, or in any other application where bandwidth savings are important.
SSB-FM systems analyzed in the literature use the Hilbert transform to generate a signal which is simultaneously amplitude and frequency modulated, both components being single-sideband; see, for example, the article "SSB-FM: When should You Use It?", Electronic Design, July 8, 1971, pp. 74-75. The disadvantage of the approach suggested in this article is that the circuitry is complex and the system becomes wasteful of power as the modulation index is increased.